Dental furnace



N. THOMPSON DENTAL FURNACE Aug.2, 1932.

Filed Aug. 9, 1929 2 Sheets-Sheet 1 Aug. 2, 1 932.

N. THOMPSON 1,869,831

DENTAL FURNACE 2 Sheets-Sheet 2 Filed Aug. 9, y1929 meme Aupa, iaz

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UNI-TED s'rA'rEs- PATENT 4ori-len Ol' CHICAGO, ILLINOIS, ASSIGNOB -TOCOE` LABORATORIES, INC., OF CHICAGO, ILLINOIS, A CORPORATION Ol ILLINOISI nmrrar. rUaNaca Application aled August l, 1929. Serial lo. 384,857.

This invention relates to dental furnaces and may be characterized as animprovement in dental furnaces of the type illustrated and described inmy copendng application, Se rial No. 321,016, filed November 21, 1928.

While these furnaces are referred to in the above application as beingarticularly suitable for fusing porcelain ental work, it is to beunderstood that the present invention is not limited to use withparticular materials, but may be employed as suitable or` desired. v

The object of the present invention is to eliminate the platinumwindings or coils heretofore commonly employed in devices of this sort.I have found that these windings" are rather short lived andthat it is adifficult matter to provide for their renewal without renewing eitherthe entire mulile or the.

entire lining employed in connection therewith.

Another object is to (provide a generally improved, simplified aninexpensive heater that will not burn out as uickly as the heater coilsheretofore employe and a heater that may be renewed in whole or in partconveniently and expeditiously.

Another object is to provide an improved muilleor oven structure,together with an improved lining and an improved mounting therefor.

According to the present invention, the heater is composed of elementswhich are,

referably, in the form of bars of carborundum or a carborundum com oundor other equivalent material having t .e desired heat resistingproperties. Bars of this sort are now known on the market as glow barsand these bars are suitable for the purpose of this invention. Accordingto the resent invention, I arrange a pair of these ars vertically withinthe interior of the mule chamber and a third or bridging bar of thissort is arranged horizontally across and connects the upper ends vof thevertical bars forming an inverted generally U-shaped heater.

Another object of the present invention is the provision of amuiile,which will accommodate the heater bars and which will direct theheat radiation therefrom, preferably to a substantially common center orto a substantially common field in which field the porcelain dental workor other material is adapted to be disposed.

Another object is to provide a uniform tem erature within the muiilechamber. This is o vtained by an even radiation of the heat through thechamber and by, making the chamber of such contour and proportionsrelative the work carrier receiving opening that this uniformity inradiation is obtained and not interfered with. This uniformity has notbeen obtained in other dental furnaces.

The furnace of the present invention is preferably provided with asuitable liner and the bottom of the muilie preferably has a suitablebale plate. y The lower ends of the vertical bars preferably extend downthrough the bame plate for connection in the electrical heater circuitand, where the bridging bar is disposed above the top of the liner, theupper ends of the vertical bars preferably extend through the top of theliner for contact with the bridging bar. In order to dissipate andprevent the collection of heat and injury to or burnin out of the heaterbars, articularly along t e openings through the Eaiile' at the bottomand along the o enings through the liner at the top or eit er of them, Iprovide for maintaining cool areas around the bars at these points andfor effectively dissipating the heat along these regions. 4

Some dental materials, with which the present furnace is adapted foruse, require the application of a temperature of the order of 2400 F. to2500 F. in the neighborhood of four minutes for fusion and the furnaceof the present invention is adapted to provide and withstand suchtemperatures.

Other objects and advantages of the present invention will appear fromthe following detailed description, taken in connection with theaccompanying drawings, in which:

Figure 1 is a top plan view of a furnace embodying the presentinvention;

Figure 2 is an end view,taken from the. right in Figure 1, with the baseof the furof Figure 1;

nace in elevation and the muile in section on the line 2-2 of Figure 1;

Figure 3 is a front elevational view of the furnace with the base of thefurnace in elevation and the mule in section on the line 3--3 Figure 4is a diagram ofthe electrical circuit of the furnace; Y

Figurel 5 is a fragmentary detailed section showing the contact andsupporting arm for 'one of the vertical heater bars.

Figure' 6 is a fragmentary detail section taken .on the line 6-6 ofFigure-1.

Referring to lthe drawings, 10 designates a suitably enclosed base,supported upon a bottom base plate 11 and covered by a top plate 12. Theplates 11 and 12 are preferably of suitable insulating material, such'aslber, asbestos hoard, or the like. The bottom of the base plate 11 isprovided with supporting feet 13, which may be in the form of buffersupports.

Secured at their lower ends at 14 u en the top plate 12 and projectingupward y from the plate 12 are a pair of hollow posts or standards 15supporting the mulle or vertical oven 16. The muile 16 comprises anendless generally elliptical open base 17, a baille plate 18 preferablyformed of fire clay or some other suitablehigh refractory material, an

. inner liner 19 also preferably formed of fire clay or some othersuitable high refractory material, a surrounding jacket 20 ,of suitableinsulating material, such as asbestos liber, Sil-O-Cel, or the like, ametal shell 21 enclosing the jacket 20 and the outer peripher of thebame plate 18 and a cover 22, whic may be of sheet metal and preferablyhas a marginally ,depending ange 23 telescoping over the upper end ofthe shell 21. The shell v. 21 is secured at its upper end in thedepending and endless molding-like part 23 by screws 24 and the lowerend of the shell 21 is secured in the base band 17 by screws 25. Thebase, which as pointed out, is preferably in the form of a generallyelliptical open figure, has marginally thickened openings 28 and, asshown in Figure 6,'the upper ends of the standards 15 are solid and ofreduced diameter, as indicated at 29. l

These reduced ends fit through openings 28 and support the base 17 andthereby the muftle 16 upon the standards 15. Set screws lvmay bethreaded through the outer wall of the channel section for securingthebase upin the upper reduced ends of the standar s.

The lining 19 is in the form of an inverted generally cup-shaped memberof enerally elliptical horizontal section with its inner peripherydefining a generally elliptical muffle or oven chamber 35 and its outerperiphery fitting relatively closely in a Icavity or recess 36 formed inthe jacket` 20 and of generally elliptical contour conforming with theThe heater is composed of elements in the form of bars of carborundum ora carborundum compound or other suitable or equivav lent material havingthe desired heat resisting properties. Bars of this ,sort are, asalready pointed out, now known on the market as glow bars and thesebarsare suitable for the purpose of this invention, so that a furtherdetailed description of the material or composition of these bars isbelieved unnecessary here., According to the present invention, Iarrange a and 41 vertically within the interior of the chamber 35 and athird or bridging bar 42 of this sort is arranged horizontally acrossand connects the upper endsl of the bars 40 and 41 forming an invertedgenerally U shaped heater. y I

The bridging bar 42 is disposed above the top 43 of the lining 19 andthe top 43 has openings 44 through which the upper ends of the bars 40and 41 have access to and good contact withl the bar 42. The lower endsof the bars 40 and 41 extend down through pair of these bars 40 openings46 in the baiile plate 18 and are I supported and connected into theelectrical circuit at their lower ends by metallic spring arms 48. Inorder to dissipate and prevent I the collection of heat and injury to orburning out of the heater bars 40 and 41, particularly along theopenings 44 and 46, the openings 44 and 46 are preferably tapered, asshown. The tapering of the openings 44 vand 46 removes the walls of thelining 19 from the barsl 40 and 41 along these openings, so that heat isnot confined along these areas of the bars, such as might occur if theopenin 44 and 46 conformed more closely with t e bars. In this manner,cool areas are maintained along the bars at these points and the heat iseffectively dissipated along these rehgions ofthe bars.

As already pointed out, some dental materials, with which the presentfurnace is adapted for use, require the application of tem ratures offrom 2400o F. to 2500 F.

in t e neighborhood of four minutes for fusion. For example, the S. S.White dental porcelain requires the application of a tem- .turing,andwill effectively insulate and keep the heat within the chamber 35under such temperatures and the heater bars 40, 41 and 42 will stand upunder temperatures up 2500 F. without burning out. This materiallyincreases the utility of the resent furnace and adapts the same forental work under conditions `which latinum wound muflles would notvwithstand.)

The upper wall 43 of the lining 19 is preferably depressed to space itfrom the horizontal heater bar 42 and this space is preferably filledwith a` suitable insulating material at 50. I find that providing thisinsulation 50 between the heater bar 42 and the top wall 43 of the lininprovides a protection for the bar 42, so t iat this bar will not beheated materially-from the heat of the furnace compartment 35, that is,it will not be heated materially beyond its own heatin action and itslife is thereby prolonged. he bar 42 serves as an electrical connectoracross the upper ends of the heater bars 40 and 41 and l'preferablywithout material heating action in itself.

The contact and supporting arms may be secured to the base 17, each by abolt 52, as a5y shown in Figure 5. The bolt 52 has a head -53vdisposedin a socket 53a in the base 17 with an insulating washer 535 between it4and the integral flange 53o on the base 17 at the 4lower end of thesocket and around the opening 53d through which the shank Iof the bolt52 passes with a space 53e between it and the flange 53o. The contactarm 48 is provided with an aperture 54 through which the pin 52 extendsand an insulating washer 55 is interposed between the mounted end of.the arm and the base of the channel with a nut 55 threaded upon thebolt 52 and adapted for clamping the bolt 52 and washers 53b and 55 inplace.

' A wing or thumb nut 58. is threaded upon the stem 52 below the mountedend of the arm 48 and is adapted to be threaded upwardly to clamp themounted end of the arm firmly in place with the conductor 67 clampedbetween the arm 48 and the nut 58 and in good electrical contact withthe arm. The outer end of each arm 48 is cupped at.60 to receive thelower end of the respective bar or 41, which may be rounded orcorrespondingly formed for cooperation therewith. The arms 48 are,preferably, spring arms and, in addition to connecting the bars 40 and41 into lthe electrical circuit are, preferably, biased upwardly to notonly support the bars 46 and 41, but to press these ars upwardly andhold the upper en ds in good contact with the bar 42.

The upper ends "of the bars 40 and 41 may be rounded and the lowersurface of the bar 42 is, preferably, provided with depressions orpockets 62 for receiving these rounded or otherwise suitably formedupper ends of the bars 40 and 41, as shown in Figure 3.

Referring to the diagram of Figure4, the

05 device is provided with suitable binding posts fiesta# supplycircuit'66 may be connected inthe usual manner. The supply circuit maybe at 110 volts or at any other suitable voltage.

The terminal 65 ma be suitably mounted upon the base 10 and rom one ofthese terminals a conductor 67 extends as through theinterior of thebase 10, which may be enclosed by suitable vertical side and end wallslpreferably of mesh or open work construction as shown for cooling theinterior of the base. The conductor 67 leads up from the interior of thebase 10 through one of the standards 15 and out through an 'opening 68in this standard, which may-be hollow only from the bottom of thestandard up to the opening 68. The end of the conductor which' is ledout through the opening 68 is clamped as shown in Figure 5, against themounted end of the adjacent contact arm 48 by the nut 58. A secondconductor 69 extends from the interior of the base 10 up through theother standard 15 and out through an opening 70 and is similarlyconnected with the other contact arm 48. Within and housed by the base10 is a suitable resistance unit 72. This resistance unit 72 ispreferably in the form of a carbon pile resistance longitudinallydisposed in the bottom of the base 10 and prefer'- ably to one side ofthe center of the base, so as to not interfere with the action of thevertical rack bar 73, the lower end of which extends down through theupper plate 12 and into the interior ofthe base enclosure 10.

Carbon pile resistance elements of this sort are well known in the artand a detailed description of the same is believed unnecessary here.resistance element is connected (Figure 4) by a conductor 75 with theother terminal 65, while the opposite end of the resistance element l72is connected through the conductor 69 with the associated .contact arm48. -One end of the resistance element 72 is supported upon a panelelement 78, which is adapted to be secured to one of the end walls ofthe base enclosure 10, as shown in Figure 2. This panel which is alsopreferably of mesh or o n work construction and may be removable withthe resistance 72 as a unit and secured in place by screws or the like(not shown). In the illustrated embodiment a small separate removablepanel 99 is shown an o ening in the end walland internally into the aseenclosure by screws 100 as shown in Figure 3. Externally of the baseenclosure 10, the resistance element 72 is provided with E'or terminals65, to which the two sides of the Suffice it to say that one end of thisl a suitable control knob 79. By manipulating this control rod 79, thecarbon .buttons or other elementsV may be pressed more tightly lto therto reduce the resistance in the circuit and bymanipulating the controlrod or turning it in the opposite direction, for examveo ple, thepressure may be released and the carbon elements loosened with respectto each other to increase the resistance in the circuit.

A voltmeter 82 is, preferably, connected linto the electrical circuit,as shown in FigureA Lland is mounted upon the top of the baseenclosure10 for the purpose of indicatingr the voltage in the circuit. A switch83 (Figure 4) connected into the circuit is adapted for opening andclosing the circuit at will.

For the purpose of indicating whether or not there is a current flow tothe circuit when the switch is closed or o en, a pilot light 84, in theform of an incan( escent bulb, is, preferably, connected in arallel withthe circuit. This bulb 84 is, pre erably, mounted within the baseenclosure and is visi-ble from the outside through a suitable phresnol85 in the front wall of the base enclosure., as shown in Figure 3.

For the purpose of indicating, at all times, the temperature within thechamber 35, a thermo-couple 86 is mounted in the wall of the mulile 16,as shown in Figure 2. This thermo-couple passes through an insulatingsleeve 87 .fixed in the wall of the jacket 2() and its inner end extendsinto and is exposed to the temperatures within the oven or mule chamber35. A meter 88, which may-be of the galvanometer type, is disposed onthe top of and constituting a unit with the instrument 82, as shown inFigure 3, and this meter is connected through suitable leads 89 with thethermo-couple 86 for the purpose of indicating, by the osition of thepointer 90 of the meter whic may play over a suitable Y those 'skilledinthe art toclearly understand graduated scale, the'temperature withinthe compartment 35. The thermo-couple 86 and meter 88 constitute apyrorneter. The showing of these parts is more or less-diagrammatic, butis believed sufficient to enable thel association of these features withthe present invention.

The work carrier comprises a disk 92, which is preferably made of fireclay or other suitable high refractory material. The disk 92 is carriedupon the upper end of the rack bar 73, which isarranged to slide throughan opening in the top plate 12 and extends, at its lower end, down infothe base enclosure 10.v

Removably positioned upon the disk 92 is an inverted crucible 93, whichserves as a lsupport for lthe work to be baked or fused.

The crucible 93 is, preferably, formed of fire clay, alun'dum, or othersuitable high refractory material. Y i

'The rack bar 73 is moved vertically by means of pinion 94, the teeth ofwhich engage the teeth ofthe rack bar. The pinion 94 is fixed upon ashaft 95 and disposed within i the vbase enclosure 10. The shaft 95 isjourynailed in suitablebearings in the base enclosure and oneend'extends out through the 'conical portion which fits into an opening97 in the bale plate 18 and is provided with an annular flange orvshoulder at its lower l end, which engages up beneath the baflie plate.The work designated at 98 is supported upon the closed top of thecrucible and is held substantially centrall disposed withinv the mulechamber thereby, as shown in Figure 3. The interior elliptical contourof ,the lining 19 is such as to accommodate the vertical bars and 41and, at

the same time, directs the heat radiation from these bars tosubstantially a common-center, or to a common field. The crucible 93supports the work 98 at this common center or in this common field, sothat the generally elliptical internal contour of the mule not onlyaccommodates the heater-bars, but by directing the heat radiationv fromthese bars uniform temperature -within the mulile chamber. This 1s animportant aspect of the present invention.

In the operation of the furnace of the present invention, the lingerpiece 96 is turned to move the crucible 93 downwardly from the bottom ofthe muiile, so thatthe work may be placed on the top of the crucible.The-pinion 94 is then turned in the opposite direction, to elevate therack bar with an accom anyin movement of the crucible up into t e mu einto the position 'shown in Figure 3. The work 98 then occupies aposition in substantially the center of the chamber 35, whereupon therheostat or resistance element 7 2 may be adjusted by the knob 7 9 toprovide the desired resistance therethrough and the current from theline is then connected by closing the switch 83. The bars 40 and 41thereupon become highly heated and the chamber 35 is heated to a highdegree, which is indicated upon the instrument 88. The heat is directedby the inner surface of the lining 19 to the common center, in which theWork 98 is arranged and the heatin continues until the desired resultsare o tained.' When the operation is lto substantially a common center,provides a contact withfsaid bar.

ber, a hama-plate forl the open end of said chamber, said baie platehaving clienings therethrough, a pair of heater bars 'sposed alonglthesides of said chamber and extending t rough the openings in said baleplate, and means externally of said plate for supporting saidflast barsand ho 2. In an electrical furnace, a mule definin a heating chamber,closed at one end .an open at the opposite end, a heater bar extendingalong the closed end of said chamber, a baffle plate for the open end ofsaid chamber, said bale plate having openings therethrough, a pair ofheater ars di osed along the sides o' said chamber andp through theopenings in said baie plate, and means externally of said plate forsupporting said `last bars and holding same in-contact with said firstbar, said bale plateopenings being tapered to dissipate and prevent thee collection of heat along the bars adjacent their passage through thebaffle pla-te.

In witness whereof, I- hereunto subscribe my name this 1st day of July,1929.

NAT THOMPSON,

ding same 1n extending`

